How Does Cathodic Protection Stop Corrosion?

Cathodic protection prevents corrosion by converting all of the anodic (active) sites on the metal surface to cathodic (passive) sites by supplying electrical current (or free electrons) from an alternate source.

Usually this takes the form of galvanic anodes, which are more active than steel. This practice is also referred to as a sacrificial system, since the galvanic anodes sacrifice themselves to protect the structural steel or pipeline from corrosion.


In the case of aluminum anodes, the reaction at the aluminum surface is: (four aluminum ions plus twelve free electrons)
4Al => 4AL⁺⁺⁺ + 12 e^-

and at the steel surface, (oxygen gas converted to oxygen ions which combine with water to form hydroxyl ions)


3O₂ + 12e^- + 6H₂0 => 12OH^-

As long as the current (free electrons) is arriving at the cathode (steel) faster than oxygen is arriving, no corrosion will occur.

Figure 1: Sacrificial anode system in seawater

by: Richard Baxter, Jim Britton

Source: http://www.cathodicprotection101.com/